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Paper: Observations of Magnetic Fields on Late-type Stars and Brown Dwarfs
Volume: 405, Solar Polarization 5: In Honor of Jan Olof Stenflo
Page: 485
Authors: Johns-Krull, C.M.
Abstract: Magnetic fields produce activity on the Sun and cool stars. Activity itself involves both the dynamo production of magnetic fields and the magnetic heating of the outer atmosphere of these objects which produces the radiative signatures of activity. On cool pre-main sequence stars, magnetic fields truncate circumstellar disks and direct accreting disk material near the poles of the central star. In the past several years, measurements of the magnetic field strength and constraints on the field geometry have become available for a number of low mass stars and brown dwarfs. Much of the recent observational effort has centered on T Tauri stars, due to the importance of strong stellar fields in explaining this stage of star formation, and on very low mass stars and brown dwarfs where measurements of traditional activity indicators suggest sharp differences in field production and/or heating efficiency compared to what is observed in slightly higher mass stars. It is important to note that a complete picture of the fields on these objects requires both spectropolarimetric and Zeeman broadening measurements made in non-polarized light. Here, I will review the techniques for measuring the magnetic field properties of cool stars and the general trends that have emerged from these observations.
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